In some cultures, ravens have long been considered to be birds of ill omen and, in some cases, death. Due to their eery cries they have been called the ‘ghosts of murdered people’ and the ‘souls of the damned’. But what information is actually conveyed in their calls?
Ravens, as corvids, are known to possess unusually high levels of intelligence for birds and they also have a wide range of vocalizations which are mostly used for social interactions. When in the presence of a large supply of food they will use ‘haa’ calls to alert neighboring ravens to the food. Recruitment of other ravens may benefit the caller as allies could help them reduce potential dangers and overpower dominant ravens.
Researchers at the University of Vienna and the University of Cambridge studied the vocal signals emitted by ravens while they were feeding. They looked for features in food calls that might provide ravens with information about unknown individuals.
Raven ‘haa’ calls provide clues about their sex and age
Dr. Markus Böckle, the corresponding author, said: “The majority of previous research on call characteristics in ravens focused on recognition of known individuals. However, to our knowledge no experiments have tested for features in food calls that might provide ravens with information about unknown individuals.”
The authors studied a population of free-ranging common ravens that regularly gathered during the feedings of wild boar at the Cumberland Wildpark Grünau, Austria. Each feeding session was simultaneously video- and audio-recorded to identify vocalizing individuals and a total of 418 calls of 12 individuals were analyzed.
We show for the first time that ravens can potentially use food calls to tell other ravens apart.
Dr. Böckle adds: “Our results suggest that ravens have the necessary variation in their food calls and the cognitive means to distinguish between specific classes of sex and age (class-recognition). Thus, we show for the first time that ravens can potentially use food calls to tell other ravens apart, according to these categories. This gives ravens the opportunity to use information about the caller in decision making processes, such as whether to defend their territory or to join or avoid foraging groups.”
Dr. Böckle said: “It is important to note that ravens use these calls to refer to food items but at the same time transmit more information than just the presence of food. Calls referring to external objects like food are frequently thought of as precursors of language. Our results add further insights into raven intelligence and their complex feeding behavior.”
How the information helps the ravens
Ravens facing problems in accessing food are likely to use the information provided by the calls to recruit allies that will help them reduce potential dangers and overpower dominant ravens. Class-recognition of unknown callers could allow ravens to assess the degree of competition for food and decide whether to join a specific feeding situation or not.
The researchers propose that low-ranking ravens might benefit from attracting non-breeding peers when calling within a territory of a breeding raven pair. By increasing the number of non-breeders and thus overpowering the territorial pair, the recruiting ravens might secure access to food.
Furthermore, the authors suggest that juvenile ravens may profit from indicating their age to unknown individuals. Perceivers of their calls might take into account that parent ravens could be in the vicinity to defend their young.
So the next time you hear the call of a raven don’t be afraid as it’s likely they’re just hungry and looking for some friends.